1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine having a first fuel injection mechanism (an in-cylinder injector) for injecting fuel into a cylinder and a second fuel injection mechanism (an intake manifold injector) for injecting fuel into an intake manifold or an intake port, and relates particularly to a technique for making a correction for a quantity of fuel deposited on an internal wall of an intake port when a load required for the internal combustion engine is changed.
2. Description of the Background Art
An internal combustion engine having an intake manifold injector for injecting fuel into an intake manifold of the engine and an in-cylinder injector for injecting fuel into a combustion chamber of the engine, and configured to determine a fuel injection ratio between the intake manifold injector and the in-cylinder injector based on an engine speed and an engine load, is known. In this internal combustion engine, a total injection quantity corresponding to the sum of the fuel injected from both fuel injection valves is predetermined as a function of the engine load, and the total injection quantity is increased as the engine load is greater.
In such an internal combustion engine, when the engine load has exceeded a set load and a fuel injection from the intake manifold injector is initiated, part of the fuel injected from the intake manifold injector deposits on an internal wall of the intake manifold. As a result, the fuel supplied from the intake manifold to the combustion chamber of the engine is smaller in quantity than the fuel having been injected from the in-cylinder injector. Accordingly, if the fuel is injected from each of the fuel injection valves based on the injection quantity predetermined as a function of the engine load, when fuel injection from the intake manifold injector is started, a fuel quantity actually supplied to the engine combustion chamber becomes smaller than a requested fuel quantity (a lean state). Thus, a problem arises that the output torque of the engine temporarily drops.
Additionally, in such an internal combustion engine, when the engine load has dropped lower than a set load and fuel injection from the intake manifold injector is stopped, the fuel deposited on the internal wall of the intake manifold is continued to be supplied to the engine combustion chamber. As a result, if fuel is injected from each of the fuel injection valves based on the injection quantity predetermined as a function of the engine load, when fuel injection from the intake manifold injector is stopped, a fuel quantity actually supplied to the engine combustion chamber becomes greater than a requested fuel quantity (a rich state). Thus, a problem arises that the output torque of the engine temporarily rises.
Japanese Patent Laying-Open No. 5-231221 discloses a fuel injection type internal combustion engine including an in-cylinder injector for injecting fuel into a cylinder and an intake manifold injector for injecting fuel into an intake manifold or an intake port, for preventing fluctuations in engine output torque when starting and stopping port injection. The fuel injection type internal combustion engine includes a first fuel injection valve (an intake manifold injector) for injecting fuel into an engine intake manifold and a second fuel injection valve (an in-cylinder injector) for injecting the fuel into an engine combustion chamber, wherein, when an engine operation state is in a predetermined operation range, fuel injection from the first fuel injection valve is stopped, and when an engine operation state is not in the predetermined operation range, the fuel is injected from the first fuel injection valve. The fuel injection type internal combustion engine includes means for estimating a deposited fuel quantity on an intake manifold internal wall when fuel injection from the first fuel injection valve is started, and for estimating a flow-in quantity of the deposited fuel flowing into the engine combustion chamber when fuel injection from the first fuel injection valve is stopped, and means for correcting a fuel quantity injected from the second fuel injection valve to be increased by the above-mentioned deposited fuel quantity when the fuel injection from the first fuel injection valve is started, and for correcting a fuel quantity injected from the second fuel injection valve to be decreased by the above-mentioned flow-in quantity when the fuel injection from the first fuel injection valve is stopped.
According to the fuel injection type internal combustion engine, by correcting a fuel quantity injected from the second fuel injection valve to be increased by a deposited fuel quantity when fuel injection from the first fuel injection valve is started, a fuel quantity actually supplied to the engine combustion chamber satisfies a required fuel quantity; by correcting the fuel quantity injected from the second fuel injection valve to be decreased by a flow-in quantity when fuel injection from the first fuel injection valve is stopped, a fuel quantity actually supplied to the engine combustion chamber satisfies a required fuel quantity. As a result, in either case of starting and stopping the fuel supply from the first fuel injection valve, a fuel quantity supplied to engine combustion chamber satisfies a required fuel quantity, and therefore the engine output torque is prevented from being fluctuated.
However, in the fuel injection type internal combustion engine disclosed in Japanese Patent Laying-Open No. 5-231221, a fuel quantity injected from the second fuel injection valve (in-cylinder injector) is corrected, only when fuel injection from the first fuel injection valve (intake manifold injector) that has not been performed is started, or when fuel injection from the first fuel injection valve (intake manifold injector) that has been performed is stopped. Specifically, it addresses: the case where DI ratio r (a ratio of a quantity of fuel injected from the in-cylinder injector to a total quantity of the fuel being injected) changes from 1 (from a state where fuel is injected solely from the in-cylinder injector to a state where fuel injection from the intake manifold injector is started); or the case where DI ratio r changes from 0 (from a state where the fuel is injected solely from the intake manifold injector to a state where fuel injection from the in-cylinder injector is started). Here, the wall deposited fuel associated with turning ON/OFF of the intake manifold injector is corrected using the in-cylinder injector. Thus, as the correction of the wall-deposited fuel is made using the in-cylinder injector, and not the intake manifold injector that has caused the deposit, a fuel injection quantity from the in-cylinder injector is affected by a correction quantity (a correction to increase and a correction to decrease) and the DI ratio greatly deviates from the ratio calculated under the operation conditions of the internal combustion engine.